The initial induction of self-reactive T cell by self-antigen is a critical checkpoint in development of autoimmunity. Conditions present during this primary T cell activation step can have permanent effects on the character of T cell development. Recently, it has become evident that the T helper phenotype (e.g. Th1/Th2) of self antigen reactive CD4+ T cells can either promote or suppress the development of autoimmune diseases including insulin dependent diabetes mellitus. Our focus over the past 3 years has been the regulation of Th1/Th2 phenotype development. Our studies have contributed to the understanding of Th1/Th2 development, being the first group to utilize TCR-transgenic models to study Th1/2 regulation. We identified cytokines, particularly IL-12, that direct Th1 development from naive T cells and have determined the capacities of distinct antigen presenting cells (APCs) to initiate these responses. We have-begun studies of the molecular regulation of the genes that control these processes. The specific aims of this proposal are to: 1. Examine cellular basis of Th1/Th2 development. We will develop a new system to examine influence of peptide/MHC structure on Th1/Th2 development while continuing our work on cytokines and antigen presenting cells (APCs) in this process, focusing on IL-12 and IFN-gamma. 2. Examine intracellular mechanisms of Th1/Th2 development. Our demonstration that IL-12 induces Th1 development led us to examine intracellular signalling pathways for IL-12 in developing T cells. We identified a novel IL-l2 induced pathway operative in Th1 but not Th2 cells that activates a Stat3/Stat4 containing nuclear complex, which we name NFIL-12. We propose to examine the role of this pathway and NFIL-12 in Th1 development. 3. Study Th1/Th2 development in the context of NOD mice. We will examine the role of Th1/Th2 regulation in the development of insulin dependent diabetes mellitus (IDDM) in the NOD model. In conjunction with this, we will construct an alpha-betaTCR transgenic system in the NOD mouse expressing the TCR from an islet antigen reactive diabetogenic CD4 T cell. We will examine the regulation of Th1 and Th2 phenotypes of this clone and determine the effect on diabetogenic potential. This CD4 TCR transgenic line will be used collaboratively with another CD8 TCR transgenic system produced in PROJECT 1 of this program by Drs. Unanue and Kanagawa.